Sikera Ušum

Arrogant King's Alcohol. The second Noble Phantasm of Assassin of “Red,” Semiramis. Its effect turns the surrounding environment into poison. Not only does it give a poison attribute to all attacks, it can also add poison to even the air and mana itself. It is her certain-kill Noble Phantasm as an Assassin. If a Servant has an anecdote in their legend where they withstood poison, they will receive a bonus to their resistance against this Noble Phantasm, but on the other hand, those who have anecdotes of having been killed by poison have their resistance to it go down.
Furthermore, when Semiramis is within the “Hanging Gardens of Babylon: Aerial Gardens of Vanity,” she can even summon creatures of the Phantasmal Races if they have an anecdote related to poison.
If she were summoned as a normal Assassin without the skill “Double Summon,” Semiramis wouldn't be able to use the “Hanging Gardens of Babylon,” so she would use this Noble Phantasm as her main weapon instead.

Fate/Apocrypha material: Fate/Apocrypha Encylopedia